Dew point and relative humidity, along with temperature and wind, are crucial measures to predicting how you will feel.

https://en.wikipedia.org/wiki/Dew_point

https://en.wikipedia.org/wiki/Humidity#Relative_humidity

In the US, the 100th meridian is a popular demarcation for the half of the country that experiences high humidity versus the other half that experiences low humidity. It is why 100F in Phoenix, Arizona is much more tolerable than 100F in Atlanta, Georgia.

https://en.wikipedia.org/wiki/100th_meridian_west